Piezoelectric/electrostrictive element and piezoelectric/electrostrictive device and production method thereof

ABSTRACT

The piezoelectric/electrostrictive element includes: a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces, the first and second surfaces being inclined at given angles to one of the narrower and wider surfaces, said laminate being made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes each of which is disposed between adjacent two of the piezoelectric/electrostrictive layers, the internal electrodes being broken up into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers; a first external electrode formed on the first surface of said laminate, said first external electrodes being coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes. Since it is of a substantially trapezoidal shape which decreases in width from one of the bottom surfaces to the other bottom surface, the angle which the slant surfaces of both sides make with the other bottom surface is obtuse, thus resulting in an increase in strength of a ridge portion (a corner) defined by the other bottom surface and the slant surfaces. When the other bottom surface of the piezoelectric/electrostrictive element is secured on a movable plate (diaphragm) by adhesive, a recess-shaped (V-groove shaped) gap defined by the movable plate and the slant surfaces of both the sides of the piezoelectric/electrostrictive element can be filled with the adhesive, thereby resulting in a further increase in force (bonding strength) which secures the piezoelectric/electrostrictive element to the movable plate. The existence of the adhesive in the recess-shaped gap offers the effect of avoiding removal of the piezoelectric/electrostrictive element from the movable plate even if the stress arising from a difference in thermal expansion between the piezoelectric/electrostrictive element and the movable plate is produced.

USE FIELD OF THE INVENTION

[0001] The present invention relates generally to apiezoelectric/electrostrictive element, a piezoelectric/electrostrictivedevice and a production method thereof, and more particularly to alaminated piezoelectric/electrostrictive element and a laminatedpiezoelectric/electrostrictive device made up ofpiezoelectric/electrostrictive layers and internal electrode layerslaminated alternately, and a production method thereof.

PRIOR ART

[0002] In recent years, a variety of fields such as optics, magneticrecording, precision machining, and printing demand a displacementelement for controlling, for example, the length or position of anoptical path in the order of a submicron or vibrations precisely. Assuch a displacement element meeting the above demand, there is oneemploying displacement provided by a reverse piezoelectric effect or anelectrostrictive effect taken place when the voltage is applied to apiezoelectric/electrostrictive material made of, for example, aferroelectric substance.

[0003] Conventionally, as such a displacement element, a laminatedpiezoelectric element 100, as shown in FIG. 34, which is disclosed inJapanese Patent First Publication No. 4-309274 is known. Thepiezoelectric/electrostrictive element 100 includes, as shown in FIG.34, a lamination 104 formed by laminating a plurality of piezoelectricceramic layers 101 and electrode layers 102 alternately and a pair ofelectrically insulated external electrodes 104 and 105 which connect theelectrode layers 102 alternately on opposed side surfaces of thelaminate 103 and are so formed as to extend to upper and lower surfacesof the laminate 103. In the laminated piezoelectric element 100, ridgesdefined by the side surfaces and the upper and lower surfaces of thelaminate 103 are rounded to an extent where the radius of curvature ofthe ridges exceeds half the thickness of the piezoelectric ceramiclayers 101.

[0004] The production of the laminated piezoelectric element 100 shownin FIG. 34 is accomplished by first weighing and grinding raw material,mixing it with binder, and defoaming the mixture, after which themixture is shaped into a sheet from which rectangular green sheets 101Aare punched (which will be the piezoelectric ceramic layers 101 bybaking). A conductive paste is printed over a given area of one surfaceof the green sheet 101A to form the electrode layer 102. Next, the greensheets 101A on which the electrode layers 102 are printed properly are,as shown in FIG. 35, laminated and bonded by pressure and cut as neededafter which it is baked to produce the laminate 103 as shown in FIG. 36.As a result, the green sheets 101A are, as mentioned above, baked toproduce the piezoelectric ceramic layers 101. In the laminate 103,arrangement positions of the electrode layers 102 are predetermined on apair of opposed side surfaces thereof so that the electrode layers 102may be exposed alternately. Afterwards, on given areas of upper andlower surfaces of the thus produced laminate 103, an external uppersurface electrode 104A, and an external lower surface electrode 105A areformed. Next, on a pair of opposed side surfaces 106 and 107 to whichthe electrode layers 102 of the laminate 103 are exposed alternately,external side surface electrodes (thick film electrodes) 104B and 105Bare formed to make the laminated piezoelectric element 100 show in FIG.34. The external side surface electrode 104B is so formed as to connectwith the external upper surface electrode 104A, while the external sidesurface electrode 105B is so formed as to connect with the externallower surface electrode 105A. As a method of forming the above mentionedexternal electrodes 104 and 105, there is a dipping method or anevaporation method.

[0005]FIG. 37 shows an actuator 200 utilizing the thus constructedlaminated piezoelectric element 100. The actuator 200 has the laminatedpiezoelectric element 100 secured on a movable plate (diaphragm) 110 byan adhesive 111.

[0006] As another displacement element, a piezoelectric displacementelement, as disclosed in Japanese Patent First Publication No.63-295269, is known which is equipped with a plurality of opposed innerelectrode layers in a ceramic thin plate exhibiting the piezoelectriceffect. Corners that are boundaries of side surfaces and upper and lowersurfaces of the ceramic thin plate are chamfered mechanically. On frontand reverse surfaces and the opposed side surfaces of the ceramic thinplate, a pair of opposed surface electrodes connecting with internalelectrode layers is so formed that the electrodes are electricallyinsulated from each other. The opposed surface electrodes are formed onthe surfaces of the ceramic thin plate by a physical vapor depositionmethod such as a sputtering method or a vapor deposition method or afilm forming method such as plating.

SUMMARY OF THE INVENTION

[0007] The laminated piezoelectric element 100, as shown in FIG. 34, hasproblems in that the possibility that edges of the green sheets. 101Aare deformed, damaged, or broken by handling is high. Particularly, athin piezoelectric element in which a total film thickness (thickness)of the laminate 103 is 100 μm or less has a high possibility that thegreen sheets 101A are broken by handling. The conventional laminatedpiezoelectric element 100, thus, has a problem that the fabricationyield is low.

[0008] The piezoelectric displacement element, as disclosed in JapanesePatent First Publication No. 63-295269 is chamfered by mechanicallycutting end portions of the ceramic thin film diagonally, which resultsin an increase in production processes. The mechanical cutting may alsocause damage to the ceramic thin film.

[0009] The invention was made in order to solve the above problems. Itis, thus, an object of the invention to provide apiezoelectric/electrostrictive element and apiezoelectric/electrostrictive device which are excellent in strength,shock resistance, handling, dimensional accuracy, positional accuracy,stability of element characteristics, and fabrication yield, and toprovide a production method thereof.

[0010] In order to solve the above problems, the first feature of theinvention lies in a piezoelectric/electrostrictive element comprising: asubstantially trapezoidal laminate having narrower and wider surfaceslying substantially in parallel to each other and first and secondsurfaces opposed to each other between the narrower and wider surfaces,the first and second surfaces being inclined at given angles to one ofthe narrower and wider surfaces, said laminate being made up of aplurality of piezoelectric/electrostrictive layers and a plurality ofinternal electrodes each of which is disposed between adjacent two ofthe piezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes.

[0011] The thus constructed piezoelectric/electrostrictive element is ofa substantially trapezoidal shape which decreases in width from one ofthe bottom surfaces to the other bottom surface, so that the angle whichthe slant surfaces of both sides make with the other bottom surface isobtuse, thus resulting in an increase in strength of a ridge portion (acorner) defined by the other bottom surface and the slant surfaces.Therefore, for example, when the other (narrower) bottom surface issecured: on a movable plate (diaphragm), the breakage or damage of saidridge portion caused by an external force or vibrations of thepiezoelectric/electrostrictive element itself is avoided. When the otherbottom surface of the piezoelectric/electrostrictive element is securedon the movable plate (diaphragm) by adhesive, a recess-shaped (V-grooveshaped) gap defined by the movable plate and the slant surfaces of boththe sides of the piezoelectric/electrostrictive element can be filledwith the adhesive, thereby resulting in a further increase in force(bonding strength) which secures the piezoelectric/electrostrictiveelement to the movable plate. The existence of the adhesive in therecess-shaped gap offers the effect of avoiding removal of thepiezoelectric/electrostrictive element from the movable plate even ifthe stress arising from a difference in thermal expansion between thepiezoelectric/electrostrictive element and the movable plate isproduced.

[0012] The piezoelectric/electrostrictive layers are decreased in widthgradually in one of directions of lamination. Thus, for example, whenthe external electrode layers, the piezoelectric/electrostrictivelayers, and the internal electrode layers are laminated in a givenorder, it is possible to pile up the piezoelectric/electrostrictivelayers on a backing layer stably. Therefore, when the external electrodelayers, the piezoelectric/electrostrictive layers, and the internalelectrode layers are laminated by printing using, for example, a screenprinting method, the printing is achieved easily since a lower one ofthe piezoelectric/electrostrictive layers has an area greater than thatof an upper one of the piezoelectric/electrostrictive layers. The screenprinting method makes it possible to apply, for example, a conductivepaste, the external electrode layers to the slant surface (a sidesurface portion) of the laminate.

[0013] Both the external electrode layers formed on said side surfaceportions extend along the wider surface of said laminate, therebyensuring a joint area (a pad portion) which establishes a joint of wiresfor applying a drive voltage to the external electrode layers or wiresfor detecting a produced voltage, which facilitates connection of thewires. Particularly, as described above, when the narrower bottomsurface of the laminate is secured on the movable plate, it is possibleto bond the wires on a sufficient area of the wider bottom surface. Thewidth of one of the external electrode layers extending on the widerbottom surface of the laminate is greater, thereby allowing the one ofthe external electrode layers to be used as a voltage applying electrodeor a voltage detecting electrode.

[0014] Additionally, one of the surfaces of thepiezoelectric/electrostrictive element may be formed by apiezoelectric/electrostrictive layer to increase a bonding strengthusing adhesive has the affinity to the piezoelectric/electrostrictivelayers, for example, when the side of the piezoelectric/electrostrictivelayer is bonded to the movable plate.

[0015] The second feature of the invention lies in apiezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes and in which saidpiezoelectric/electrostrictive element is bonded to a surface of amovable plate on a side of the narrower surface of said laminate.

[0016] In the piezoelectric/electrostrictive device, the narrower bottomsurface of the laminate is bonded to the surface of the movable plate,so that a corner portion having an obtuse angle defined by the narrowerbottom surface and both side surface portions engages the movable plate.The corner having the obtuse angle will have strength greater than acorner having an acute angle or a right angle and offers the effect ofincreasing the durability such as the strength or shock resistance ofthe piezoelectric/electrostrictive device.

[0017] A gap (recess) formed by both the side surface portions of thepiezoelectric/electrostrictive device and the movable plate defines aliquid sump of adhesive having flowability prior to solidification andworks to absorb an excess or a lack of the adhesive caused by avariation in quantity of the applied adhesive or undulations of themovable plate and the piezoelectric/electrostrictive element. Theapplication of a proper quantity of the adhesive to a suitable area ofthe movable plate will enable automatic alignment of thepiezoelectric/electrostrictive element with a proper position with aidof an effect such as surface tension of the adhesive within the gap.

[0018] Additionally, filling the gap with the adhesive enables firminstallation of the piezoelectric/electrostrictive element on themovable plate. If the adhesive with which the gap is filled keeps theelasticity after being solidified, it alleviates the stress arising froma difference in thermal expansion between the movable plate and thepiezoelectric/electrostrictive element, thereby avoiding removable ofthe piezoelectric/electrostrictive element from the movable plate.Specifically, the filling of the gap defined by the side portions of thepiezoelectric/electrostrictive element and the movable plate with theadhesive will restrict a reduction in strength to fix thepiezoelectric/electrostrictive element even if thepiezoelectric/electrostrictive element is decreased in size.

[0019] Further, the external electrode layers formed on both the sidesurface portions of the piezoelectric/electrostrictive element extend onthe wider bottom surface of the laminate, thus providing a joint areasufficient for establishing connection of external wires to the externalelectrode layers.

[0020] The movable plate is made of a conductive material. One of theexternal electrode layers of the piezoelectric/electrostrictive elementis connected to the movable plate, thereby increasing a wiring space ofthe other external electrode layer and facilitating ease of a connectingoperation.

[0021] The third feature of the invention lies in a method of producinga piezoelectric/electrostrictive element comprising the steps of:

[0022] a first step of preparing a ceramic substrate having a givenwidth;

[0023] a second step of forming a laminate on said ceramic substrate,said laminate being made up of a first and a second portions laid tooverlap each other, the first portion being made by the steps of:

[0024] printing a first electrode layer and a second electrode layer onsaid ceramic substrate which are disposed at a given interval away fromeach other;

[0025] forming a piezoelectric/electrostrictive layer using apiezoelectric/electrostrictive paste on the first and second electrodelayers so as to cover portions of the first and second electrode layersother than edge portions thereof lying outward in a widthwise directionof said ceramic substrate;

[0026] forming a first electrode layer on an upper surface and a sidesurface of the piezoelectric/electrostrictive layer so as to establishan electric connection only with the first electrode layer lyingimmediately beneath the first electrode layer formed in this step,

[0027] said second portion being made by performing the following set ofsteps a given number of times which include:

[0028] forming a piezoelectric/electrostrictive layer using apiezoelectric/electrostrictive paste on an uppermost one of the firstelectrode layers, the piezoelectric/electrostrictive layer formed inthis step having a width smaller than that of thepiezoelectric/electrostrictive layer lying immediately beneath thepiezoelectric/electrostrictive layer formed in this step;

[0029] forming a second electrode layer on an upper surface and a sidesurface of an uppermost one of the piezoelectric/electrostrictive layersso as to establish an electric connection only with the second electrodelayer lying immediately beneath the second electrode layer formed inthis step;

[0030] forming a piezoelectric/electrostrictive layer using apiezoelectric/electrostrictive paste on an uppermost one of the secondelectrode layers, the piezoelectric/electrostrictive layer formed inthis step having a width smaller than that of thepiezoelectric/electrostrictive layer lying immediately beneath thepiezoelectric/electrostrictive layer formed in this step;

[0031] forming a first electrode layer on an upper surface and a sidesurface of an uppermost one of the piezoelectric/electrostrictive layersso as to establish an electric connection only with the first electrodelayer lying immediately beneath the first electrode layer formed in thisstep; and

[0032] a third step of baking said ceramic substrate and said laminateat a given temperature; and

[0033] a fourth step of removing said laminate from said ceramicsubstrate.

[0034] In the method of producing the thus constructedpiezoelectric/electrostrictive element according to the third feature,it is possible to pile up the piezoelectric/electrostrictive layers byprinting so that areas thereof decrease gradually, thus resulting inease of manufacture. The piezoelectric/electrostrictive layers, thefirst electrode material layer, and the second electrode material layermay be formed in a printing method, thus allowing thepiezoelectric/electrostrictive element to be produced which is higher indimensional accuracy and positional accuracy and less susceptible toadverse effects such shifting during transportation and deformationcaused by the transportation and eliminating the need for process oftransporting and piling up the piezoelectric/electrostrictive layers,which avoids the breakage or damage of thepiezoelectric/electrostrictive layers caused by handling thereof.

[0035] The formation of portions which become continuous external sidesurface electrodes on both sides of the laminate is achieved in sequenceby repeating printing of the first and second electrode material layers,thus eliminating the need for a process of forming additional externalside surface electrode.

[0036] Further, a film which disappears upon baking of the laminate ispreformed on a ceramic substrate used in producing thepiezoelectric/electrostrictive element, thereby resulting in easyremoval of the piezoelectric/electrostrictive element from the ceramicsubstrate when baked.

[0037] In this invention, the external side surface electrode whichdefines an outermost contour of the piezoelectric/electrostrictiveelement as viewed in a plane may be formed by printing with highpositional accuracy. For example, when thepiezoelectric/electrostrictive element is positioned by positioning pinsto mount the piezoelectric/electrostrictive element on a movable plate,it is possible to arrange the piezoelectric electrostrictive elementwith high positional accuracy.

[0038] The fourth feature of the invention lies in a method of producinga piezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes, and the piezoelectric/electrostrictiveelement is bonded to a surface of a movable plate by adhesive.

[0039] In the method of producing the thus constructedpiezoelectric/electrostrictive device, the narrower bottom surface sideof the laminate is bonded to the movable plate through the adhesive,thus facilitating ease of filling a gap (recess) defined by slants ofboth side surfaces of the piezoelectric/electrostrictive element and themovable plate with the adhesive. This allows the gap to be filled withthe adhesive in quantity suitable for the size of the gap, thus ensuringthe bonding strength. When piezoelectric/electrostrictive elements arejoined to each other, gaps (recesses) are also formed by side surfaceportions of the piezoelectric/electrostrictive elements, thus offering asimilar effect of increasing the bonding strength.

[0040] The narrower bottom surface of the piezoelectric/electrostrictiveelement is bonded to the movable plate, so that angles which the sidesurface portions of the piezoelectric/electrostrictive element make withthe movable plate will be obtuse, thus providing the effect of avoidinglocal breakage or damage of the piezoelectric/electrostrictive element.The same is true for a case where piezoelectric/electrostrictiveelements are bonded at narrower bottom surfaces to each other.

[0041] Automatic positioning of the piezoelectric/electrostrictiveelement is achieved by setting a coefficient of viscosity of theadhesive applied on the surface of the movable plate to a given value toenable the gaps (recesses) defined by the slants of the side surfaces ofthe piezoelectric/electrostrictive element and the movable plate to befilled with the adhesive.

BRIEF DESPCRIPTION OF THE DRAWINGS

[0042]FIG. 1 is a perspective view which shows apiezoelectric/electrostrictive element according to the first embodimentof the invention;

[0043]FIG. 2 is a plan view of a piezoelectric/electrostrictive elementaccording to the first embodiment of the invention;

[0044]FIG. 3 is a bottom view of a piezoelectric/electrostrictiveelement according to the first embodiment of the invention;

[0045]FIG. 4 is a cross-sectional elevation on section line A-A of FIG.2;

[0046]FIG. 5 is a side view of a piezoelectric/electrostrictive deviceaccording to the first embodiment of the invention;

[0047]FIG. 6 is a plan view of a piezoelectric/electrostrictive deviceaccording to the first embodiment of the invention;

[0048]FIG. 7 is an explanatory side view which represents usage of apiezoelectric/electrostrictive device according to the first embodimentof the invention;

[0049]FIG. 8 is an explanatory side view which shows a modifiedembodiment 1 of a piezoelectric/electrostrictive device according to thefirst embodiment of the invention;

[0050]FIG. 9 is an explanatory side view which shows a modifiedembodiment 2 of a piezoelectric/electrostrictive device according to thefirst embodiment of the invention;

[0051]FIG. 10 is an explanatory side view which shows a modifiedembodiment 3 of a piezoelectric/electrostrictive device according to thefirst embodiment of the invention;

[0052]FIG. 11 is an explanatory side view which shows a modifiedembodiment 4 of a piezoelectric/electrostrictive device according to thefirst embodiment of the invention;

[0053]FIG. 12 is a plan view which illustrates a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

[0054]FIG. 13 is a side view which illustrates a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

[0055]FIG. 14 is a plan view which illustrates a production method of apiezoelectric/electrostrictive element according to the first embodimentof the invention;

[0056]FIG. 15 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0057]FIG. 16 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0058]FIG. 17 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0059]FIG. 18 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0060]FIG. 19 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0061]FIG. 20 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0062]FIG. 21 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0063]FIG. 22 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0064]FIG. 23 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0065]FIG. 24 is a process sectional view which shows a productionmethod of a piezoelectric/electrostrictive element according to thefirst embodiment of the invention;

[0066]FIG. 25 is a side view of a piezoelectric/electrostrictive elementaccording to the second embodiment of the invention;

[0067]FIG. 26 is a plan view of a piezoelectric/electrostrictive elementaccording to the second embodiment of the invention;

[0068]FIG. 27 is a side view of a piezoelectric/electrostrictive deviceaccording to the second embodiment of the invention;

[0069]FIG. 28 is a plan view which represents a production method of apiezoelectric/electrostrictive device according to the second embodimentof the invention;

[0070]FIG. 29 is a plan view which represents a production method of apiezoelectric/electrostrictive device according to the second embodimentof the invention;

[0071]FIG. 30 is a plan view which illustrates a movable platepositioning jig used in a production method of apiezoelectric/electrostrictive device according to the second embodimentof the invention;

[0072]FIG. 31 is a side view which illustrates a movable platepositioning jig used in a production method of apiezoelectric/electrostrictive device according to the second embodimentof the invention;

[0073]FIG. 32 is a plan view which illustrates an element positioningjig use in a production method of a piezoelectric/electrostrictivedevice according to the second embodiment of the invention;

[0074]FIG. 33 is a side view which shows a combination of illustrates amovable plate positioning jig and an element positioning jig used in aproduction method of a piezoelectric/electrostrictive device accordingto the second embodiment of the invention;

[0075]FIG. 34 is a perspective view which shows a conventionalpiezoelectric/electrostrictive element;

[0076]FIG. 35 is a perspective view which shows a production process ofa conventional piezoelectric/electrostrictive element;

[0077]FIG. 36 is a perspective view which shows a laminate of aconventional piezoelectric/electrostrictive element;

[0078]FIG. 37 is a side view which shows a conventionalpiezoelectric/electrostrictive device;

[0079]FIG. 38 is an explanatory plan view which shows positioning of aconventional piezoelectric/electrostrictive element; and

[0080]FIG. 39 is an enlarged major part side view of a conventionalpiezoelectric/electrostrictive element.

DETAILED DESCRIPTION OF EMBODIMENTS

[0081] A piezoelectric/electrostrictive element, apiezoelectric/electrostrictive device, and a production method thereofwill be explained in detail with reference to embodiments as illustratedin the drawings. The attention should be paid to the fact that thedrawings are schematic, and the thickness and a film thickness ratio ofmaterial layers are different from actual ones. Practical thickness ordimensions should be decided with reference to the followingexplanation. Of course, parts whose dimensional relation and ratio aredifferent from each other are included in the several drawings.

[0082] The piezoelectric/electrostrictive element and thepiezoelectric/electrostrictive device according to the inventionincludes an element which converts electric energy into mechanicalenergy, or vice versa by reverse the piezoelectric effect, theelectrostrictive effect, or the piezoelectric effect and a deviceequipped with the same and may be employed as passive elements such asacceleration sensors or impact sensors utilizing the piezoelectriceffect as well as active elements such as a variety of actuators ortransducers, especially displacement elements using displacement by thereverse piezoelectric effect or the electrostrictive effect.

[0083] [First Embodiment of the Invention]

[0084] (Piezoelectric/Electrostrictive Element)

[0085] First, an outline of a structure of apiezoelectric/electrostrictive elemnet of this embodiment will bedescribed using FIGS. 1 to 4. The piezoelectric/electrostrictive element10 of this embodiment, as shown in FIG. 1, includes, for example, fourpiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D, forexample, three internal electrode layers 12A, 12B, and 12C interposedbetween adjacent two of the piezoelectric/electrostrictive layers 11A,11B, 11C, and 11D, and a pair of external electrode layers 14 and 15 towhich the external electrode layers 12A, 12B, and 12C connectalternately. The piezoelectric/electrostrictive element 10 has asubstantially trapezoidal laminated structure in which-upper and loweropposed bottom surfaces are both rectangular.

[0086] As shown in FIG. 1, an area of one of the bottom surfaces (uppersurface) f1 of the piezoelectric/electrostrictive element 10 is widerthan that of the other bottom surface (lower surface) f2. As shown inFIG. 1, the width of the wider bottom surface f1 (i.e., the length in anarrow direction as expressed by x in the drawing) is W1, and the lengththereof (i.e., the length in an arrow direction as expressed by y in thedrawing) is L1. FIG. 2 is a plan view which shows the wider bottomsurface f1. FIG. 3 is a bottom illustration of thepiezoelectric/electrostrictive element 10 as viewed from the side of thenarrower bottom surface f2. The narrower bottom surface f2 of thepiezoelectric/electrostrictive element 10 is illustrated in FIG. 3. Asshown in FIG. 3, the width of the bottom surface f2 is W2 that issmaller than the width W1 of the bottom surface f1. The length of thebottom surface f2 is equal to the length L1 of the bottom surface f1.

[0087] As can be seen from the bottom illustration of FIG. 3, both sideedges of the bottom surface f2 are located inward from both side edgesof the bottom surface f1 by the same distance W3 and overlap with thebottom surface f1 in a lengthwise direction. Thepiezoelectric/electrostrictive element 10, thus, has slant surfaces f3and f4, as shown in FIGS. 1 and 3, formed on the sides thereof in thedirection x. The pair of slant surfaces f3 and f4 are inclined in adirection in which they approach each other from the wider bottomsurface f1 to the narrower bottom surface f2.

[0088] The external structure of the piezoelectric/electrostrictiveelement 10 has been explained above. Next, the structure and positionalrelation of parts making up the piezoelectric/electrostrictive element10 will be explained in detail using FIGS. 1 to 4. FIG. 4 is across-sectional view on section line A-A of FIG. 2.

[0089] In the piezoelectric/electrostrictive element 10 according tothis embodiment, the piezoelectric/electrostrictive layers 11A, 11B,11C, and 11D are made of, for example, lead zirconium titanate (PZT).When formed by PZT, the strength of the piezoelectric/electrostrictivelayers 11A, 11B, 11C, and 11D is on the order of 70 MPa. The internalelectrode layers 12A, 12B, and 12C and the external electrode layers 14and 15 are made of, for example, platinum (Pt).

[0090] In the piezoelectric/electrostrictive element 10, thepiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D which arelaminated from the bottom surface f1 to the bottom surface f2 decreasein width gradually, so that the whole of thepiezoelectric/electrostrictive element 10 has, as mentioned above, theslant surfaces f3 and f4 formed on the side portions.

[0091] Between the piezoelectric/electrostrictive layers 11A and 11B,the internal electrode layer 12A is disposed which extends from theslant surface f3 to the slant surface f4. The internal electrode 12Adoes not reach the slant surface f4. Between thepiezoelectric/electrostrictive layers 11B and 11C, the internalelectrode layer 12B is disposed which extends from the slant surface f4to the slant surface f3. The internal electrode 12B does not reach theslant surface f3. Between the piezoelectric/electrostrictive layers 11Cand 11D, the internal electrode layer 12C is disposed which extends,like the above described internal electrode layer 12A, from the slantsurface f3 to the slant surface f4. It is advisable that the end edgesof the above described internal electrodes 12A and 12C on the side ofthe slant surface f4 lie at the same location as viewed on a plane andoverlap vertically, however, the internal electrode layer 12C may beshorter in the x direction along the slant surface f4.

[0092] Further, slant portions 14A and 15A of the external electrodelayers 14 and 15 are formed on the slant surfaces f3 and f4. In thisembodiment, the width of the slant portion 14A (i.e., the length in adirection of slant surface inclination) is greater than that of theslant portion 15A. The slant portion 14A is, as shown in FIG. 4, soformed as to cover the whole of the slant surface f4, therebyestablishing connection of the slant portion 14A of the externalelectrode layer 14 to the internal electrode layer 12B and connection ofthe slant portion 15A of the external electrode layer 15 to the internalelectrode layers 12A and 12C. Specifically, the external electrodelayers 15 and 14 are so constructed as to connect with the internalelectrode layers 12A, 12B, and 12C alternately.

[0093] On an upper surface (i.e., an outer surface) of the widestpiezoelectric/electrostrictive layer 11A, upper surface portions 14B and15B of the external electrode layers 14 and 15 are, as shown in FIG. 1,formed which extend from x-direction side edges of the outer surface ofthe piezoelectric/electrostrictive layer 11A so as to approach eachother. The upper surface portions 14B and 15B of the external electrodelayers 14 and 15 are separate from each other on the side of one of theedge portions. Specifically, in this embodiment, the width (i.e., thelength in the x direction) of the upper surface portion 14B of theexternal electrode layer 14 is greater than that of the externalelectrode layer 15. The edge of the upper surface portion 14B of theexternal electrode layer 14 on the side of the slant surface f3 lies atthe same location as that of the edge of the above described internalelectrode layer 12B as viewed on a plane, but however, it is not limitedto the same.

[0094] On a lower surface (i.e., an outer surface) of the narrowestpiezoelectric/electrostrictive layer 11D, the lower surface portion 14Cof the external electrode layer 14 is formed. The lower surface portion14C is so formed as to extend from a lower edge of the slant surface 14Ato the slant surface f3. An edge of the lower surface portion 14C on theside of the slant surface f3 is so set as to lie at the same location asthat of an edge of the internal electrode layer 12B as viewed on aplane, however, it is not limited to the same.

[0095] In this embodiment, the piezoelectric/electrostrictive layers11A, 11B, 11C, and 11D are four layers. The internal electrode layers12A, 12B, and 12C are three layers. The upper surface portion 14B andthe lower surface portion 14C of the external electrode layer 14 are soarranged on the upper and lower surfaces of thepiezoelectric/electrostrictive element 10 as to function as opposedelectrodes, however, the number of the layers and the number of theinternal electrode layers connecting with the external electrode layers14 and 15, respectively, may be equal to each other or not. The numberof the electrode layers are determined in terms of relations to a drivevoltage and the degree of displacement of a movable plate, as will bedescribed later. An increase in total number of thepiezoelectric/electrostrictive layers will cause a driving force drivingthe movable plate on which the piezoelectric/electrostrictive element 10is installed to be increased, thus enabling a greater displacement andresult in an increase in rigidity of the piezoelectric/electrostrictiveelement 10, thereby increasing the resonance frequency, which allows thespeed of a displacement operation to be increased easily.

[0096] As a practical material of the piezoelectric/electrostrictivelayers 11A, 11B, 11C, and 11D in this embodiment, ceramic may be usedwhich contains one or a mixture of lead zirconate, lead titanate, leadmagnesium-niobate, lead nickel niobate, lead zinc niobate, leadmanganese niobate, lead antimony stannate, lead manganese tungstate,lead cobalt niobate, barium titanate, sodium bismuth titanate, kaliumsodium niobate, and strontium bismuth tantalate in addition to the abovedescribed lead zirconium titanate (PZT).

[0097] Particularly, material whose main components are lead zirconate,lead titanate, and lead magnesium niobate or material whose maincomponent is sodium bismuth titanate have high electromechanicalcoupling factor and piezoelectric constant, are low in reactivity to afiring setter (in this case, ceramic oxide such as zirconia, alumina, ormagnesia), and provide stable compositions when thepiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D).

[0098] Further, one or some of oxides such as lanthanum (La), calcium(Ca), strontium (Sr), molybdenum (Mo), tungsten (W), barium (Ba),niobium (Nb), zinc (Zn), nickel (Ni), manganese (Mn), cerium (Ce),cadmium (Cd), chromium (Cr), cobalt (Co), antimony (Sb), iron (Fe),yttrium (Y), tantalum (Ta), lithium (Li), bismuth (Bi), and tin (Sn) maybe mixed with the above described ceramic material.

[0099] Additionally, for example, lanthanum (La) and strontium (Sr) maybe added to main components of lead zirconate, lead titanate, and leadmagnesium niobate for providing the advantage that it is possible toadjust the coercive electric field and piezoelectric characteristics.

[0100] The addition of an easy-to-vitrify material such as silica ispreferably avoided. The reason for this is that material such as silicareacts easily with a piezoelectric/electrostrictive material during heattreatment (i.e., firing) of the piezoelectric/electrostrictive layers11A, 11B, 11C, and 11D and change components thereof, thus resulting inthe deterioration of piezoelectric characteristics.

[0101] As the piezoelectric/electrostrictive layers 11A, 11B, 11C, and11D, the above described variety of piezoelectric ceramics arepreferably used, but electrostrictive ceramics, ferroelectric ceramicsor antiferroelectric ceramics may be employed. However, in a case wherethe piezoelectric/electrostrictive element 10 is used to position amagnetic head of a hard disc drive, the linearity to the amount ofdisplacement of moving parts, a drive voltage, or an output voltage isimportant. The use of material that is smaller in electric-field strainhysteresis is, thus, preferable. Specifically, material having acoercive electric field of 10 kV/mm or less is preferably used.

[0102] The external electrode layers 14 and 15 is preferably made ofmetal which is solid at room temperature and excellent in conductivity.As such a metal, in addition to the above described platinum (Pt), oneof aluminum (Al), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo),ruthenium (Ru), palladium (Pd), rhodium (Rh), silver (Ag), tin (Sn),tantalum (Ta), tungsten (W), iridium (Ir), gold (Au), and lead (Pb) oran alloy thereof may be used. A cermet material in which the samematerial as that of the piezoelectric/electrostrictive layers 11A, 11B,11C, and 11D is dispersed in the above materials may be used.

[0103] The selection of materials of the external electrode layers 14and 15 and the internal electrode layers 12A, 12B, and 12C of thepiezoelectric/electrostrictive element 10 is determined depending upon amethod of forming the piezoelectric/electrostrictive layers 11A, 11B,11C, and 11D. The method of forming the piezoelectric/electrostrictivelayers will be described later.

[0104] In the thus constructed piezoelectric/electrostrictive element10, corners (ridge portions) 16 and 17 of both widthwise sides of thelower surface f2, as shown in FIG. 4, have obtuse angles. Specifically,the arigles which the lower surface f2 makes with the slant surfaces f3and f4 are obtuse, so that the corners 16 and 17 have a greater strengthas compared with corners having right angles or acute angles. Theincrease in strength of the corners 16 and 17 serves to avoid the damageor breakage of the corners 16 and 17 caused by an external force orvibrations of the piezoelectric/electrostrictive element 10 when thelower surface f2 of the piezoelectric/electrostrictive element 10 isinstalled on a movable plate (i.e. a diaphragm).

[0105] The upper surface portions 14B and 15B of the external electrodelayers 14 and 15 are both disposed on the side of the wider bottomsurface f1, thus allowing the upper surface portions 14B and 15B to beused as connection areas (i.e., pad portions), which facilitatesconnection of wires.

[0106] (Piezoelectric/Electrostrictive Device)

[0107] Next, an embodiment of a piezoelectric/electrostrictive device 20employing the piezoelectric/electrostrictive element 10 according to thefirst embodiment will be described using FIGS. 5 to 7. FIG. 5 is a sideview of the piezoelectric/electrostrictive device 20. FIG. 6 is a planview of the piezoelectric/electrostrictive device 20.

[0108] The piezoelectric/electrostrictive device 20 is constructed to beof a unimorph type wherein the narrower lower surface f1 of the abovedescribed piezoelectric/electrostrictive element 10 is joined to amovable plate (diaphragm) 21 using adhesive 22. In thepiezoelectric/electrostrictive device 20 according to this embodiment,the piezoelectric/electrostrictive element 10 is substantially identicalin width (i.e., the length in a y direction, as expressed by an arrow inFIG. 6) with the movable plate 21. The length (i.e., the length in an xdirection, as expressed by an arrow in FIG. 6) of the movable plate 21is set longer than that of the piezoelectric/electrostrictive element10. The movable plate 21 may have flexibility and mechanical strengthwhich withstands breakage caused by bending. Material may be selected interms of the response and operationability.

[0109] In the piezoelectric/electrostrictive device 20, the adhesive 22is interposed between an upper surface of the movable plate 21 and abottom surface (lower surface) and the slant surfaces f3 and f4 of thepiezoelectric/electrostrictive element 10 to bond thepiezoelectric/electrostrictive element 10 on the upper surface of themovable plate 21. Particularly, V groove-shaped gaps defined between theslant surfaces f3 and f4 of the piezoelectric/electrostrictive element10 and the upper surface of the movable plate 21 are filled with theadhesive 22. As a result, the shape defined by thepiezoelectric/electrostrictive element 10 and the adhesive 22 will besubstantially trapezoidal or rectangular.

[0110] The movable plate 21 is a portion which operates based on drivingof the piezoelectric/electrostrictive element 10 and has a variety ofparts installed thereon according to the purpose of use of thepiezoelectric/electrostrictive device 20. For instance, in a case wherethe piezoelectric/electrostrictive device 20 is used as a displacementelement, a shielding plate of an optical shutter etc. are installed. Ina case where the piezoelectric/electrostrictive device 20 is employed toposition a magnetic head of a hard disc drive or in a ringing inhibitingmechanism, parts such as a magnetic head, a slider with the magnetichead, or a suspension with a slider which are required to be positionedare installed.

[0111] As material of the movable plate 21, ceramic including zirconiais preferable. Particularly, material containing a main component ofstabilized zirconia or partially stabilized zirconia is desirable as thematerial of the movable plate 21 because it exhibits a greatermechanical strength and toughness if shaped to have a thin wall.

[0112] When the movable plate 21 is made of a metallic material, it ispreferably flexible or bendable. For example, as ferrous materials, avariety of stainless steels or a variety of spring steels are desirable.As non-ferrous materials, beryllium copper, phosphor bronze, nickel, ornickel-iron alloy is desirable.

[0113] In the thus constructed piezoelectric/electrostrictive device 20,the V groove-shaped gaps defined by the slant surfaces f3 and f4 and theupper surface of the movable plate 21 are formed on both sides of thepiezoelectric/electrostrictive element 10 and work as a liquid sumps forthe adhesive 22 that is liquid or pastelike. The adhesive 22 held in thegaps is solidified while being kept lump by the surface tension, therebypreventing the adhesive 22 from overflowing to or around the upper sideof the piezoelectric/electrostrictive element 10 or the lower side ofthe movable plate 21. The V groove-shaped gaps defined by the slantsurfaces f3 and f4 of the piezoelectric/electrostrictive element 10 andthe upper surface of the movable plate 21 may be filled with theadhesive 22 in proper quantities by determining the quantity of theadhesive 22 to be applied to the movable plate 21 to a predeterminedvalue.

[0114] The side corners of the lower surface f2 of thepiezoelectric/electrostrictive element 10 both have, as described above,obtuse angles, and thus have a greater strength as compared with whenthey have right angles or acute angles. The increase in strength of thecorners 16 and 17 serves to avoid the damage or breakage of the corners16 and 17 caused by vibrations of the piezoelectric/electrostrictiveelement 10 or external forces.

[0115] Further, the stress arising from a thermal expansion differencebetween the piezoelectric/electrostrictive element 10 and the movableplate 21 is maximized near the ends of the piezoelectricelectrostrictive element 10, but the adhesive 22 in the V groove-shapedgaps works to hold the adhesive strength and reduce the stress becauseof a low elasticity of the adhesive, thereby avoiding breakage andremoval of the piezoelectric element 10 from the movable plate 21.

[0116] The upper surface portions 14B and 15B of the external electrodelayers 14 and 15 are arranged on the side of the wider bottom surface f1(i.e., on the same plane), thereby facilitating connection of wire tothe upper surface portions 14B and 15B.

[0117] In a case where the thus constructedpiezoelectric/electrostrictive device 20 is used as an active device,wires 23 and 24 may be connected to the upper surface portion 14B of theexternal electrode layer 14 and the upper surface portion 15B of theexternal electrode layer 15 formed on the bottom surface f1,respectively, and to a voltage applying circuit 25. Such an activedevice may be employed as transducers, actuators, frequency domainfunctional parts (filters), transformers, vibrators or resonators forcommunications or power sources, oscillators, or discriminators. Thewires 23 and. 24 are provided preferably by a flexible printed circuit(FPC), flexible flat cables (FFC), bonding wires.

[0118] In a case where the piezoelectric/electrostrictive device 20 isused as a passive device, the wires 23 and 24 may be connected to avoltage detecting circuit 26 instead of the voltage applying circuit 25.In the case where the wires 23 and 24 are joined to the upper surfaceportions 14B and 15B of the external electrode layers 14 and 15 of thepiezoelectric/electrostrictive element 10, it is advisable that theadhesive 22 have electric insulation ability. Such a passive device maybe employed as ultrasonic sensors, acceleration sensors, angular ratesensors, shock sensors., or mass sensors.

[0119] (Modified Embodiment 1 of Piezoelectric/Electrostrictive Device)

[0120]FIG. 8 is an explanatory side view which illustrates the modifiedembodiment 1 of the piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive element 10 according to the firstembodiment. The structure of the modified embodiment 1 will be explainedwith the same reference numbers assigned to the same parts of themodified embodiment 1 as those of the above describedpiezoelectric/electrostrictive device 20 and similar reference numbersassigned to similar parts thereof.

[0121] The piezoelectric/electrostrictive device 20A according-to themodified embodiment 1 has the narrower bottom surface f2 of the abovedescribed piezoelectric/electrostrictive element 10 bonded and securedto the upper surface of the movable plate 21 having the conductivityusing the adhesive 22 having the conductivity.

[0122] In the modified embodiment 1, the lower surface portion 14C and alower portion of the slant surface 14A of the external electrode layer14 formed on the bottom surface f2 of the piezoelectric/electrostrictiveelement 10 are joined to and secured on the movable plate 21 through theadhesive 22A. The adhesive 22A is set so as not to extend over the slantsurface 15A of the external electrode layer 15. This is achieved bydetermining the quantity of the adhesive 22A to be applied to themovable plate 21 properly.

[0123] In the thus constructed piezoelectric/electrostrictive device20A, the wire 23 is joined to the movable plate 21, and the wire 24 iscoupled to the upper surface portion 15B of the external electrode layer15. The use of the piezoelectric/electrostrictive device 20A as anactive device may be achieved by connecting the wires 23 and 24, asshown in FIG. 8, to the voltage applying circuit 25. The use of thepiezoelectric/electrostrictive device 20A as a passive device may beachieved by connecting the wires 23 and 24, as shown in FIG. 8, to thevoltage detecting circuit 26.

[0124] As the adhesive 22 having the conductivity, a variety ofconductive bonds including metallic fillers or anisotropic conductivebonds used in the field of semiconductor packaging may be selectedproperly.

[0125] The movable plate 21 having the conductivity may be made of ametallic material that is flexible or bendable. For example, as ferrousmaterials, a variety of stainless steels or a variety of spring steelsare desirable. As non-ferrous materials, beryllium copper, phosphorbronze, nickel, or nickel-iron alloy is desirable.

[0126] (Modified Embodiment 2 of Piezoelectric/Electrostrictive Device)

[0127]FIG. 9 is a side view which illustrates the modified embodiment 2of the piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive elements 10 according to the firstembodiment. The structure of the modified embodiment 2 will be explainedwith the same reference numbers assigned to the same parts of themodified embodiment 2 as those of the above describedpiezoelectric/electrostrictive device 20 and similar reference numbersassigned to similar parts thereof.

[0128] The piezoelectric/electrostrictive device 20B according to themodified embodiment 2 has a bimorph type structure in which the aboveconstructed piezoelectric/electrostrictive element 10 is secured on eachsurface of the single movable plate 21 by the adhesive 22. The narrowerbottom surfaces of the piezoelectric electrostrictive elements 10 areplaced in contact with the respective surfaces of the movable plate 21and bonded so that the movable plate 21 is sandwiched therebetween.

[0129] In the piezoelectric/electrostrictive device 20B according to themodified embodiment 2, wires may be connected to the upper surfaceportions 14B and 15B of the external electrode layers 14 and 15 of eachof the piezoelectric/electrostrictive elements 10. Alternatively, themovable plate 21 may be used as a common electrode of thepiezoelectric/electrostrictive elements 10, and a wire may be connectedonly to the upper surface portion 15B of each of thepiezoelectric/electrostrictive element 10.

[0130] The assembly of the piezoelectric/electrostrictive elements 10may be of a symmetrical type (a series type) in which the directions ofpolarization are symmetrical with respect to the movable plate 21 or anasymmetrical type (a parallel type) in which the directions ofpolarization of the piezoelectric/electrostrictive elements 10 are thesame.

[0131] (Modified Embodiment 3 of Piezoelectric Electrostrictive Device)

[0132]FIG. 10 is a side view which illustrates the modified embodiment 3of the piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive elements 10 according to the firstembodiment. The structure of the modified embodiment 2 will be explainedusing the same reference numbers assigned to the same parts as those ofthe above described piezoelectric/electrostrictive device 20 and similarreference numbers assigned to similar parts.

[0133] In the piezoelectric/electrostrictive device 20C according to themodified embodiment 3, a pair of piezoelectric/electrostrictive elements10 are so arranged that the narrower bottom surfaces f2 thereof areopposed to each other and bonded to each other through the adhesive 22.The piezoelectric/electrostrictive device 20C has a bimorph typestructure which is not equipped with a movable plate.

[0134] In the modified embodiment 3, the assembly of thepiezoelectric/electrostrictive elements 10, like the above describedmodified embodiment 2, may be of the symmetrical type (the series type)or the asymmetrical type (the parallel type).

[0135] (Modified Embodiment 4 of Piezoelectric/Electrostrictive Device)

[0136]FIG. 11 is a side view which illustrates the modified embodiment 4of the piezoelectric/electrostrictive device using thepiezoelectric/electrostrictive elements 10 according to the firstembodiment.

[0137] The piezoelectric/electrostrictive device 20D according to themodified embodiment 4, as shown in FIG. 11, includes a base body 30which has movable plate portions 31 and a fixing portion 32 formedintegrally. The movable plate portions 31 are opposed to each withthrough a given gap. The fixing portion 32 is interposed between themovable plate portions 31 on the same side of ends of the movable plateportions 31. The piezoelectric/electrostrictive device 20D has thepiezoelectric/electrostrictive elements 10 bonded and secured to opposedoutside surfaces on the same side of end portions of the pair of movableplate portions 31.

[0138] The piezoelectric/electrostrictive device 20D has the structurein which the movable plate portions 31 are displaced by driving thepiezoelectric/electrostrictive elements 10, or the displacement of themovable plate portions 31 is detected by thepiezoelectric/electrostrictive elements 10. For instance, in thepiezoelectric/electrostrictive device 20D shown in FIG. 11, the movableplate portions 31 and the piezoelectric/electrostrictive elements 10constitute actuator portions 33. On the other ends of the movable plateportions 31, movable portions 34 are-formed which are so formed as tohave thick walls projecting inwardly. The movable portions 34 aredisplaced following displacing operations of the movable plate portions31.

[0139] The base body 30 may be made of metal or ceramic as a whole orhave a hybrid structure made of a combination of metal and ceramic. Thebase body 30 may also have a structure in which respective parts arebonded by adhesive such as organic resin or glass, a ceramic one-piecestructure made of a fired ceramic green laminate, or a metallicone-piece structure formed integrally by brazing, soldering, eutecticbonding, or welding. It is advisable that the base body 30 be made of aceramic laminate formed integrally by firing a ceramic green laminate.Such ceramic one-piece members are of a structure which has highreliability of joints and is excellent in ensuring the rigidity and easyto manufacture.

[0140] The piezoelectric/electrostrictive elements 10 are bonded andsecured to outside surfaces on the same side of the end portions of thebase body 30 through the adhesive 22. The adhesive 22 may be an organicadhesive or inorganic adhesive. The piezoelectric/electrostrictiveelements 10 are bonded at the narrower bottom surfaces f2 to the basebody 30. The V groove-shaped gaps defined by the slant surfaces f3 andf4 of the piezoelectric/electrostrictive elements 10 and the externalsurfaces of the base body 30 are filled with the adhesive 22. As aresult, the shape defined by the piezoelectric/electrostrictive elements10 and the adhesive 22 will be substantially trapezoidal or rectangularparallelepipedic.

[0141] On the wider bottom surfaces f1 of thepiezoelectric/electrostrictive elements 10, the upper surface portions14B of the external electrode layers 0.14 and the upper surface portions15B of the external electrode layers 15 are disposed away from eachother while keeping electric insulation. A wire is, thus, bonded to theupper surface portions 14B and 15B which is to be joined to a voltageapplying circuit or a voltage detecting circuit which is not shown.

[0142] A gap (air), as shown in FIG. 11, may be defined between theopposed end surfaces 34A of the pair of movable portions 34.Alternatively, a plurality of members made of material identical with ordifferent from that of the movable portions 34 may be disposed betweenthe opposed end surfaces 34A.

[0143] In the thus constructed piezoelectric/electrostrictive device20D, the movable portions 34, the movable plate portions 31, and thefixing portion 32 that define the basic structure are formed integrallyby a tough material. The piezoelectric/electrostrictive device 20D,therefore, has the advantages that it is higher in mechanical strength,excellent in handling, impact resistance, and moisture resistance, andless susceptible to harmful vibrations (e.g., residual vibrations ornoise during high-speed operation) as compared with apiezoelectric/electrostrictive device in which all parts are made of apiezoelectric/electrostrictive material that is fragile and relativelyheavy.

[0144] The formation of the gap between the opposed end surfaces 34A ofthe movable portions 34 of the piezoelectric/electrostrictive device 20Dprovides the flexibility of the movable portion 34 including one of theend surfaces 34A and the movable portion 34 including the other endsurface 34A, so that a deformation limit to which thepiezoelectric/electrostrictive device is not broken will be high. Thepiezoelectric/electrostrictive device 20D, therefore, has the advantagethat it is excellent in handling.

[0145] In the piezoelectric/electrostrictive device 20D, the movableportions 34 are portions which operate, as described above, based on theamount of displacement of the movable plate portions 31 and have avariety of parts installed thereon according to the purpose of use ofthe piezoelectric/electrostrictive device 20D. For instance, in a casewhere the piezoelectric/electrostrictive device 20D is used as adisplacement element, for example, a shielding plate of an opticalshutter is installed. In a case where the piezoelectric/electrostrictivedevice 20D is employed to position a magnetic head of a hard disc driveor in a ringing inhibiting mechanism, parts requiring positioning of themagnetic head, a slider with the magnetic head, or a suspension with aslider are installed.

[0146] The fixing portion 32 is, as described above, a portionsupporting the movable plate portions 31 and the movable portions 34.For instance, in a case of use in positioning a magnetic head of a harddisc drive, the fixing portion 32 may be installed on a carriage armmounted on a voice coil motor (VCM), a mount plate attached to thecarriage arm, or a suspension to fix the whole of thepiezoelectric/electrostrictive device 20D.

[0147] Further, in this modified embodiment, the movable plate portions31 are portions driven by the displacement of thepiezoelectric/electrostrictive elements 10 and thus are thin plate likemembers having the flexibility and work to perform a function ofamplifying as a bending displacement an expansion/contractiondisplacement of the piezoelectric/electrostrictive elements 10 disposedon the surface thereof to transfer it to the movable portions 34.Therefore, the shape and material of the movable plate portions 31 whichonly exhibit the flexibility and mechanical strength less susceptible tobreakage caused by the bending displacement may be selected properly interms of response and operationability of the movable portions 34.

[0148] The movable plates 31 are preferably made of ceramics includingzirconia. Of the ceramics, material containing a main component ofstabilized zirconia and material containing a main component ofpartially stabilized zirconia are desirable in terms of a greatermechanical strength and a higher toughness even though a wall thicknessis small.

[0149] If the movable plate 31 is made of a metallic material, it ispreferably flexible or bendable. For example, as ferrous materials, avariety of stainless steels or a variety of spring steels are desirable.As non-ferrous materials, beryllium copper, phosphor bronze, nickel, ornickel-iron alloy is desirable.

[0150] As the above described stabilized and partially stabilizedzirconia, the following stabilized or partially stabilized ones arepreferable. Specifically, as compounds stabilizing or partiallystabilizing zirconia, there are yttrium oxide, ytteribium oxide, ceriumoxide, calcium oxide, and magnesium oxide. The desired stabilization ofzirconia may be achieved by adding at least one of the above compoundsor a mixture thereof to the zirconia.

[0151] Added amounts of yttrium oxide and ytteribium oxide are 1 to 30mol %, preferably 1.5 to 10 mol %. An added amount of cerium oxide is 6to 50 mol %, preferably 8 to 20 mol %. Added amounts of calcium oxideand magnesium oxide is 5 to 40 mol %, preferably 5 to 20 mol %. Ofthese, yttrium oxide is preferably used as a stabilizer. In the casewhere yttrium oxide is used as a stabilizer, the amount thereof ispreferably 1.5 to 10 mol % and more preferably 2 to 4 mol %.

[0152] In order to obtain the mechanical strength and stabilized crystalphase, the mean crystal grain size is 0.05 to 3 μm, preferably 1 μm orless. As described above, the movable plate portion 31, like the movableportion 34 and the fixing portion 32, may be made of ceramic. The use ofsubstantially the same material is advantageous to improve thereliability of joints and the strength of thepiezoelectric/electrostrictive device 20D and alleviate the complexityof manufacture.

[0153] Production Method of Piezoelectric/Electrostrictive Element ofthe First Embodiment)

[0154] Next, a production method of the piezoelectric/electrostrictiveelement 10 according to the first embodiment will be described belowusing FIGS. 12 to 24. The production method will be discussed whilecomparing and associating new reference numbers of respective materiallayers with reference numbers of the piezoelectric/electrostrictiveelement 10 that is a finished product as shown in FIGS. 1 to 4.

[0155] (1) First, a ceramic substrate 41, as shown in FIG. 12, isprepared which has a give size and is made of oxide such as zirconia,alumina, or magnesia. The ceramic substrate 41 functions as a table forscreen printing and a firing substrate. Incidentally, the ceramicsubstrate 41 measures approximately 40 mm×50 mm×0.3 mm.

[0156] (2) Carbon powder or a theobromine powder-dispersed paste isprinted using a 360 mesh metal screen having an emulsion film thicknessof 10 μm on a row of areas on the ceramic substarte 41 which have awidth greater than that of the piezoelectric/electrostrictive element 10and then dried to form, as shown in FIG. 12, a row of disappearing films42. Each of the disappearing films 42 contains a plurality ofelement-forming areas in an x direction. FIG. 13 is a cross section onsection line B-B of FIG. 12. The disappearing films 42 will disappear byfiring in a subsequent process to perform the function of facilitatingremoval of the piezoelectric/electrostrictive elements 10 from theceramic substrate 41. A printing direction of the disappearing films 42is a direction as illustrated by an arrow x in FIG. 12.

[0157] (3) Next, a platinum (Pt) paste is printed in a direction, asindicated by arrow y in FIG. 14, using screens (printing plates) 43A, asillustrated by hatching, and dried. The screens 43A is set to 360 inmesh and 5% m in emulsion film thickness. In this process, portionscorresponding to the upper surface portions 14B and 153 of the externalelectrode layers 14 and 15 of the piezoelectric/electrostrictive element10 of the first embodiment are printed. The use of the screen 43A, asillustrated by hatching in FIG. 14, enables simultaneous printing overthe plurality of element-forming areas along the x direction. FIG. 15shows Pt paste films 44 and 45 printed at an interval array from eachother using the screen 43A within one of the element-forming areas onthe disappearing film 42. An area including the Pt paste films 44 and 45and an intervening area is set to equal to that of a wider one of bottomsurfaces a unbaked preform of the piezoelectric/electrostrictive element10. The screen 43A, as shown in FIG. 15, works to stick an emulsion film47 to the metal screen 46 in a given pattern and transfer platinumpastes to the disappearing films 42 by pattern portions on which theemulsion layer 47 does not exist.

[0158] (4) Next, a piezoelectric paste is, as shown in FIG. 16, printedusing a screen 43B and dried to form an unbaked preform of a first oneof the piezoelectric/electrostrictive layers 11A. The screen 43B isprovided by forming the emulsion layer 47 having a thickness of 25 μm ina given pattern on the 360 mesh metal screen 46. A pattern of an openingof the emulsion layer 47 is determined to be slightly smaller than theabove described area including the Pt paste films 44 and 45 and theintervening area therebetween. For details, the unbaked preform of thepiezoelectric/electrostrictive layer 11A printed by the screen 43B arelocated at both x-direction edges inside x-direction outside edges ofthe Pt paste films 44 and 45 by a distance x1. Both y-direction sideedges of the unbaked preform of the piezoelectric/electrostrictive layer11A overlap both y-direction side edges of each of the Pt paste films 44and 45.

[0159] (5) Next, a Pt paste film 48 is, as shown in FIG. 17, printedusing a screen 43C which will be a Pt film serving as the internalelectrode layer 12A and the slant surface portion 15A of the externalelectrode layer 15 after firing and then dried. The Pt paste film 48 islaid to overlap a given length L of the Pt paste film 44 in the xdirection that is formed in the above process through the unbakedpreform of the piezoelectric/electrostrictive layer 11A. Overlappedportions of the Pt paste films 44 and 48 function as voltage-applyingelectrodes effectively.

[0160] (6) Afterwards, a piezoelectric paste is, as shown in FIG. 18,printed using a screen 43D and dried to form a unbaked preform of thepiezoelectric/electrostrictive layer 11B. One of x-direction edges ofthe unbaked preform of the piezoelectric/electrostrictive layer 11B islocated on an extension of a slant surface portion of the Pt paste film48 connecting with the Pt paste film 45. The other edge of the preformof the piezoelectric/electrostrictive layer 11B is located slightlyinside an edge of the unbaked preform of thepiezoelectric/electrostrictive layer 11A and on an extension of a slantsurface portion of the unbaked preform of thepiezoelectric/electrostrictive layer 11A.

[0161] (7) Next, a Pt paste film 49 is, as shown in FIG. 19, printedusing a screen 43E which will be a Pt paste film 49 serving as theinternal electrode layer 12B and the slant surface portion 14A of theexternal electrode layer 14 after firing and then dried. The Pt pastefilm 49 is opposed to the Pt paste film 48 through the unbaked preformof the piezoelectric/electrostrictive layer 11B. The Pt paste films 48and 49 overlap each other by the distance L in the x direction.

[0162] (8) Further, a piezoelectric paste is, as shown in FIG. 20,printed using a screen 43F which is smaller in width (length in the xdirection) than the unbaked preform of thepiezoelectric/electrostrictive layer 11B serving as ground coat and thedried to form a unbaked preform of the piezoelectric/electrostrictivelayer 11C. The unbaked preform of the piezoelectric/electrostrictivelayer 11C is slightly inside an edge of-the unbaked preform of thepiezoelectric/electrostrictive layer 11B exposed at one side from the Ptpaste film 49 and the slant surface portion of the Pt paste film 49.

[0163] (9) Afterwards, a Pt paste film 50 is, as shown in FIG. 21,printed using a screen 43G which serves as the internal electrode layer12C and the slant surface portion 15A of the external electrode layer 15after firing and then dried.

[0164] (10) Next, a Pt paste is, as shown in FIG. 22, printed using ascreen 43H and dried to form a unbaked preform of thepiezoelectric/electrostrictive layer 11D. The preform of thepiezoelectric/electrostrictive layer 11D is set smaller in width thanthe unbaked preform of the piezoelectric/electrostrictive layer 11Cserving as ground coat.

[0165] (11) Afterwards, a Pt paste film 51 is, as shown in FIG. 23,printed using a screen 43I which serves as the lower surface portion 14Cand the slant surface portion 14A of the external electrode layer 14after firing and then dried. The screen 43I as used in this process isprovided by forming the emulsion layer 47 having a thickness of 5 μl min a given pattern on the 360 mesh metal screen 46.

[0166] (12) Finally, the temperature is increased at a rate which doesnot leave organic components of each material layer and the disappearingfilms 42 to perform the firing at a maximum temperature of 1100 to 1300°C., thereby causing the disappearing films 42 to disappear, as shown inFIG. 24, to allow the piezoelectric/electrostrictive elements 10 to beremoved easily from the ceramic substrate 41.

[0167] It is possible for the production method of thepiezoelectric/electrostrictive elements 10 to pile up thepiezoelectric/electrostrictive layers 11A, 11B, 11C, and 11D in theprinting method so as to decrease in area gradually, thus resulting inease of manufacture of the piezoelectric/electrostrictive elements 10.It is also possible to form the piezoelectric/electrostrictive layers11A, 11B, 11C, and. 11D and each electrode layer (i.e., the Pt film inthis embodiment) in the printing method, thus eliminating the need forhandling and transportation. This enables the manufacture of thepiezoelectric/electrostrictive elements 10 that are higher indimensional and positional accuracy without adverse effects such asdeformation caused by the handling or the transportation.

[0168] The formation of the side portions of the laminate (i.e., bothsides in the x direction) which become the continuous externalelectrodes is achieved by forming the piezoelectric/electrostrictivelayer and the electrode layer repeatedly, thereby eliminating the needfor an additional process of forming external electrode layers,resulting in a decrease in process.

[0169] Further, easy removal of the piezoelectric/electrostrictiveelements 10 after firing is achieved by forming the disappearing films42 on the ceramic substrate 41 which will disappear by the firing priorto produce the piezoelectric/electrostrictive elements 10. Thedisappearing films 42 disappear in the firing process by sublimation andburning, thereby preventing particles from sticking to thepiezoelectric/electrostrictive elements 10.

[0170] In the production method of the piezoelectric/electrostrictiveelements, a variety of piezoelectric materials and conductive pastesthat are screen printable may be selected.

[0171] The production method of the piezoelectric/electrostrictiveelements enables the formation of the external electrode layers in theprinting method with a higher positioning accuracy, which achievesaccurate positioning of the piezoelectric/electrostrictive elements whendisposed and secured on, for example, a movable plate.

[0172] [Second Embodiment]

[0173] (Piezoelectric/Electrostrictive Element)

[0174]FIGS. 25 and 26 show a piezoelectric/electrostrictive elementaccording to the second embodiment of the invention. FIG. 25 is a sideview of the piezoelectric/electrostrictive element 60. FIG. 26 is a planview of the piezoelectric/electrostrictive element 60. Thepiezoelectric/electrostrictive element 60, as shown in the drawings,consists of four piezoelectric/electrostrictive layers 61, 62, 63, and64, upper surface electrode layers 65 and 66 formed at an interval awayfrom each other on an outside surface of thepiezoelectric/electrostrictive layer 61, internal electrode layers 67,68, 69, and 70 formed on lower surfaces of thepiezoelectric/electrostrictive layers 61, 62, 63, and 64, a slantsurface portion 71 leading to an upper surface electrode 65 inconnection with the internal electrode layers 68 and 70, a slant surfaceportion 72 leading to an upper surface electrode 66 in connection withthe internal electrode layers 67 and 69, and an insulating layer 73covering the slant surface portions 71 and 72 and the internal electrodelayer 70.

[0175] The piezoelectric/electrostrictive element 60 has a substantiallytrapezoidal laminated structure having a pair of opposed upper and lowerbottom surfaces of rectangular shape. The insulating layers 73 is madeof material which may be the same material as that of thepiezoelectric/electrostrictive layer 61 or different therefrom.

[0176] Both side edges of the bottom surface f2 are, as shown in FIG.25, located inside side edges of the bottom surface f1 by equaldistances, thereby forming slant surfaces f3 and f4 on both sides of thepiezoelectric/electrostrictive element 60 in the x direction. The slantsurfaces f3 and f4 are inclined in a direction in which they approacheach other from the wider bottom surface f1 to the narrower bottomsurface f2.

[0177] The upper surface electrode layer 65 is wider than the uppersurface electrode layer 66. The upper surface electrode layer 65 and theinternal electrode layers 68 and 70 are so formed as to extend from theslant surface portion 71 to the slant surface f4. The internal electrodelayers 67 and 69 are so formed as to extend from the slant surfaceportion 72 leading to the upper surface electrode layer 66 to the sideof the slant surface f3.

[0178] In the piezoelectric/electrostrictive element 60, areas of theupper surface electrode layer 65 and the internal electrode layers 67,68, 69, and 70 which overlap each other through thepiezoelectric/electrostrictive layers practically define voltage-appliedareas or voltage-detecting areas.

[0179] In the piezoelectric/electrostrictive element 60 of the secondembodiment, the bottom surface f2 and the slant surfaces f3 and f4 arecovered with the insulating layer 73. Wires leading to a voltageapplying circuit or a voltage detecting circuit are, thus, to beconnected to the upper surface electrode layers 65 and 66 of the bottomsurface f1.

[0180] In the piezoelectric/electrostrictive element 60 of the secondembodiment, the piezoelectric/electrostrictive layers 61, 62, 63, and 64are made of, for example, zirconium lead titanate (PZT). The internalelectrode layers 67, 68, 69, and 70, the upper surface electrode layers65 and 66, and the slant surface portions 71 and 72 are made of, forexample, platinum (Pt).

[0181] In the piezoelectric/electrostrictive element 60, thepiezoelectric/electrostrictive layers 61, 62, 63, and 64 laminated fromthe bottom surface f1 to the bottom surface f2 are decreased in width(length in the x direction) gradually. As a result, in the whole of thepiezoelectric/electrostrictive element 60, the slant surfaces f3 and f4are, as describe above, formed on the side portions.

[0182] In this embodiment, the piezoelectric/electrostrictive layers 61,62, 63, and 64 are four layers. The electrode layers holding thepiezoelectric/electrostrictive layers therebetween are five layers,however, the number of the layers and the number of the internalelectrode layers connecting with the slant surface portions 71 and 72may be equal to each other or not. The number of the electrode layersare determined in terms of relations to a drive voltage and the degreeof displacement. An increase in total number of thepiezoelectric/electrostrictive layers will cause a driving force drivingthe movable plate on which the piezoelectric/electrostrictive element 60is installed to be increased, thus enabling a greater displacement andresult in an increase in rigidity of the piezoelectric/electrostrictiveelement 60, thereby increasing the resonance frequency, which allows thespeed of a displacement operation to be increased easily.

[0183] (Piezoelectric/Electrostrictive Device)

[0184]FIG. 27 is a side view of a piezoelectric/electrostrictive device70 according to the second embodiment. Thepiezoelectric/electrostrictive device 70 is constructed to be of aunimorph type wherein the narrower bottom surface f2 of the abovedescribed piezoelectric/electrostrictive element 60 is joined to amovable plate (diaphragm) 71 using adhesive 72. In thepiezoelectric/electrostrictive device 70 of the second embodiment, themovable plate 71 is identical in width. The length of the movable plate71 is greater than that of the piezoelectric/electrostrictive element60. The movable plate 71 may have flexibility and mechanical strengthwhich withstands breakage caused by bending. Material may be selected interms of the response and operationability.

[0185] In the piezoelectric/electrostrictive device 70, the adhesive 72is interposed between an upper surface of the movable plate 71 and abottom surface (lower surface) f1 and the slant surfaces f3 and f4 ofthe piezoelectric/electrostrictive element 60 to bond thepiezoelectric/electrostrictive element 60 on the upper surface of themovable plate 71. Particularly, V groove-shaped gaps defined between theslant surfaces f3 and f4 of the piezoelectric/electrostrictive element60 and the upper surface of the movable plate 71 are filled with theadhesive 72. As a result, the shape defined by thepiezoelectric/electrostrictive element 60 and the adhesive 72 will besubstantially trapezoidal or rectangular.

[0186] The movable plate 71 is a portion which operates based on drivingof the piezoelectric/electrostrictive element 70 and has a variety ofparts installed thereon according to the purpose of use of thepiezoelectric/electrostrictive device 70. For instance, in a case wherethe piezoelectric/electrostrictive device 70 is used as a displacementelement, a shielding plate of an optical shutter etc. are installed. Ina case where the piezoelectric/electrostrictive device 70 is employed toposition a magnetic head of a hard disc drive or in a ringing inhibitingmechanism, parts such as a magnetic head, a slider with the magnetichead, or a suspension with a slider which are required to be positionedare installed.

[0187] The movable plate 71 is a portion driven by the displacement ofthe piezoelectric/electrostrictive elements 60. The movable plate 71 isa flexible member and performs a function of amplifying as a bendingdisplacement an expansion/contraction displacement of thepiezoelectric/electrostrictive elements 60 that is disposed on thesurface of the movable plate portions 71. The material of the movableplate 71 which exhibits the flexibility and mechanical strength lesssusceptible to breakage caused by the bending displacement may beselected.

[0188] As material of the movable plate 71, ceramic including zirconiais desiable. Particularly, material containing a main component ofstabilized zirconia or partially stabilized zirconia is desirable as thematerial of the movable plate 71 because it exhibits a greatermechanical strength, a high toughness, and a small reactivity to thepiezoelectric/electrostrictive layers and an electrode material ifshaped to have a thin wall.

[0189] If the movable plate 71 is made of a metallic material, it ispreferably flexible or bendable. For example, as ferrous materials, avariety of stainless steels or a variety of spring steels are desirable.As non-ferrous materials, beryllium copper, phosphor bronze, nickel, ornickel-iron alloy is desirable.

[0190] In the thus constructed piezoelectric/electrostrictive device 70,the V groove-shaped gaps defined by the slant surfaces f3 and f4 and theupper surface of the movable plate 71 are formed on both sides of thepiezoelectric/electrostrictive element 70 and work as a liquid sumps forthe adhesive 72 that is liquid or pastelike. The adhesive 72 held in thegaps is solidified while being kept lump by the surface tension, therebypreventing the adhesive 72 from overflowing to or around the upper sideof the piezoelectric/electrostrictive element 60 or the lower side ofthe movable plate 71. The V groove-shaped gaps defined by the slantsurfaces f3 and f4 of the piezoelectric/electrostrictive element 60 andthe upper surface of the movable plate 71 may be filled with theadhesive 72 in proper quantities by determining the quantity of theadhesive 72 to be applied to the movable plate 71 to a predeterminedvalue.

[0191] The side corners of the lower surface f2 of thepiezoelectric/electrostrictive element 60 both have, as described above,obtuse angles, and thus have a greater strength as compared with whenthey have right angles or acute angles. The increase in strength of thecorners serves to avoid the damage or breakage of the corners caused byvibrations of the piezoelectric/electrostrictive element 60 or externalforces when the bottom surface (lower surface) of thepiezoelectric/electrostrictive element 60 is secured on the movableplate 71.

[0192] Further, the stress arising from a thermal expansion differencebetween the piezoelectric/electrostrictive element 60 and the movableplate 71 is maximized near the ends of thepiezoelectric/electrostrictive element 60, but the adhesive 72 in the Vgroove-shaped gaps works to hold the adhesive strength and reduce thestress because of a low elasticity of the adhesive, thereby avoidingbreakage and removal of the piezoelectric element 60 from the movableplate 71.

[0193] The upper surface electrode layers 65 and 66 are arranged on theside of the wider bottom surface f1 (i.e., on the same plane), therebyfacilitating connection of wire to the upper surface electrode layers 65and 66.

[0194] When used as an active device, the thus constructedpiezoelectric/electrostrictive device 70 may be designed as atransducer, an actuator, a frequency domain functional part (a filter),a transformer, a vibrator or a resonator for communications or a powersource, an oscillator, or a discriminator. Wires may be providedpreferably by a flexible printed circuit (FPC), flexible flat cables(FFC), bonding wires.

[0195] When used as a passive device, the piezoelectric/electrostrictivedevice 70 may be designed as a ultrasonic sensor, an accelerationsensor, an angular rate sensor, a shock sensor, or a mass sensor.

[0196] In the piezoelectric/electrostrictive device 70 of the secondembodiment, the adhesive 72 sticks directly to the insulating layer 73whose surface roughness is great and which covers the bottom surface f2and the slant surfaces f3 and f4 of the piezoelectric/electrostrictiveelement 60, thus resulting in an increase in bonding strength ascompared with when the adhesive 72 sticks to a metallic electrode.

[0197] In the piezoelectric/electrostrictive device 70, by forming theupper surface electrode layers 65 and 66 of thepiezoelectric/electrostrictive element 60 in the printing method, thecontour of the widest bottom surface f1, patterns of the upper surfaceelectrode layers 65 and 66 are formed precisely, thus enabling thepositioning based on the upper surface electrode layers 65 and 66. Thisallows the piezoelectric/electrostrictive element 60 to be positionedaccurately on the movable plate 71.

[0198] The piezoelectric/electrostrictive device 70 of the secondembodiment is, as described above, of the unimorph type, but may be of abimorph type.

[0199] (Production Method of Piezoelectric/Electrostrictive Device)

[0200] A production method of a piezoelectric/electrostrictive devicewhich may be employed with the first and second embodiments will bedescribed below using FIGS. 28 to 33.

[0201] (A) First, a movable plate 80, as shown in FIG. 28, is prepared.An adhesive 81 is, as shown in FIG. 29, applied to a given position ofthe movable plate 80 using the screen printing method.

[0202] (B) Next, the movable plate 80 is, as shown in FIGS. 30 and 31,put on a movable plate positioning jig 82. The movable plate positioningjig 82 has a pair of guide pins 84 installed on side portions of amovable plate positioning substrate 83. Three vertically extendingpositioning pins 35 are installed on a central portion of the movableplate positioning substrate 83 in engagement with two sides of themovable plate 80.

[0203] (C) The piezoelectric/electrostrictive element 10 is set on anelement positioning plate 86. The element positioning plate 86 hasformed therein a plurality of vacuum openings 87 for sucking thepiezoelectric/electrostrictive element 10. Thepiezoelectric/electrostrictive element 10 is set so that the widerbottom surface f1 may be sucked by the vacuum openings 87. The elementpositioning plate 86 has formed therein guide holes 88 in which guidepins 84 are fitted when combined with the movable plate positioning jig82. The element positioning plate 86 has also formed therein openings 89for reception of the positioning pins 35 installed on the movable platepositioning jig 82.

[0204] (D) The guide pins 84 of the movable plate positioning jig 82are, as shown in FIG. 33, inserted into the guide holes 88 of theelement positioning plate 86. The element positioning plate 86 isbrought close to the movable plate positioning jig 82 to bring thepiezoelectric/electrostrictive element 10 into contact with the movableplate 80 disposed on the movable plate positioning jig 82, therebycausing the piezoelectric/electrostrictive element 10 to be bonded andsecured by the adhesive 81 applied to the movable plate 80.

[0205] (E) Afterwards, the suction by the vacuum openings 87 of theelement positioning plate 86 is stopped. The element positioning plate86 is then lifted upward to terminate the positioning of thepiezoelectric/electrostrictive element 10.

[0206] Afterwards, a weight is put on the piezoelectric/electrostrictiveelement 10 to hold it from moving during solidification of the adhesive.For example, in a case of a thermosetting one-component epoxy resinadhesive, it is put in a oven heated up to a solidifying temperature. Ina case of a UV cured adhesive, a ultraviolet ray is radiated to solidifythe bond.

[0207] In the above described piezoelectric/electrostrictive deviceproduction method, the piezoelectric/electrostrictive element 10 isbonded to one of the surfaces of the movable plate 80. In a case wherethe piezoelectric/electrostrictive elements 10 are bonded to thesurfaces of the movable plate 80, the piezoelectric/electrostrictiveelement 10 is adhered to one of the surfaces of the movable plate 80 inthe above manner, after which another movable plate positioning jig isprepared which is designed to be disposed on the movable plate 80 thatis turned over to bond the piezoelectric/electrostrictive element 10 tothe reverse surface.

[0208] In the above piezoelectric/electrostrictive device productionmethod, proper bonding may be carried out in a proper quantity of theadhesive 81, as shown in FIG. 5, by determining the quantity andthickness of the adhesive 81 to be applied to the movable plate 80 topredetermined values. It is possible to control an applied position andan applied quantity of adhesive accurately, depending upon physicalproperties (the coefficient of viscosity or thixotropy). Thus, as anapplication method of the adhesive, the screen printing method ispreferably used.

[0209] [Other Embodiments]

[0210] It should be noted that the discussion and the drawings that areparts of the disclosure of the above described first and secondembodiment of the invention do not limit the invention. From thisdisclosure, one skilled in the art will know alternative various formsof embodiments, embodiments, and working techniques.

[0211] For instance, the first and second embodiments refer to the caseswhere the number of the inner electrode layers are three and four, butit may be one, two or more, or five or more.

[0212] When produced by the printing method, thepiezoelectric/electrostrictive elements 10 and 60 have advantages ofproduction, dimensional accuracy, and positional accuracy, but even ifthe piezoelectric/electrostrictive elements 10 and 60 are not producedby the printing method, they may have the advantage of strength as longas at least the corners of the side portions of the bottom surface haveobtuse angles.

[0213] In the above described first and second embodiments, the adhesiveis put in the V groove-shaped gaps defined by thepiezoelectric/electrostrictive element and the movable plate. Theinvention may also be used in the case where only the narrower bottomsurface is bonded by adhesive.

What is claimed is:
 1. A piezoelectric/electrostrictive elementcomprising: a substantially trapezoidal laminate having narrower andwider surfaces lying substantially in parallel to each other and firstand second surfaces opposed to each other between the narrower and widersurfaces, the first and second surfaces being inclined at given anglesto one of the narrower and wider surfaces, said laminate being made upof a plurality of piezoelectric/electrostrictive layers and a pluralityof internal electrodes each of which is disposed between adjacent two ofthe piezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes.
 2. A piezoelectric/electrostrictiveelement as set forth in claim 1, wherein saidpiezoelectric/electrostrictive layers are decreased in width graduallyin one of directions of lamination.
 3. A piezoelectric/electrostrictiveelement as set forth in claim 1, wherein the external electrode layersformed on said side surface portions extend along the wider surface ofsaid laminate.
 4. A piezoelectric/electrostrictive element as set forthin claim 3, wherein a width of a portion of said first externalelectrode layer extending on said wider surface is greater than that ofa portion of said second external electrode layer extending on a side ofsaid wider surface.
 5. A piezoelectric/electrostrictive element as setforth in claim 1, wherein either of surfaces in said directions oflamination is the piezoelectric/electrostrictive layer.
 6. Apiezoelectric/electrostrictive element as set forth in claim 1, whereinthe number of said internal electrode layers connecting with said firstexternal electrode layer is identical with that of said internalelectrode layers connecting with said second external electrode layer.7. A piezoelectric/electrostrictive element as set forth in claim 1,wherein the number of said internal electrode layers connecting withsaid first external electrode layer is different from that of saidinternal electrode layers connecting with said second external electrodelayer.
 8. A piezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes and in which saidpiezoelectric/electrostrictive element is bonded to a surface of amovable plate on a side of the narrower surface of said laminate.
 9. Apiezoelectric/electrostrictive device as set forth in claim 8, whereinsaid piezoelectric/electrostrictive element is bonded to said movableplate by adhesive disposed within a gap defined by said first surface,said second surface, and said movable plate.
 10. Apiezoelectric/electrostrictive device as set forth in claim 9,characterized in that a structure made up of saidpiezoelectric/electrostrictive element and said adhesive is trapezoidalor rectangular parallelepipedic.
 11. A piezoelectric/electrostrictivedevice as set forth in claim 8, wherein the first and second externalelectrode layers formed on said first and second surfaces extend on thewider surface of said laminate.
 12. A piezoelectric/electrostrictivedevice as set forth in claim 8, wherein saidpiezoelectric/electrostrictive element is bonded only to one surface ofsaid movable plate.
 13. A piezoelectric/electrostrictive device as setforth in claim 8, wherein said piezoelectric/electrostrictive elementsare bonded to both surfaces of the movable plate so as to hold themovable plate therebetween.
 14. A piezoelectric/electrostrictive deviceas set forth in claim 8, wherein said movable plate is made of aninsulating material.
 15. A piezoelectric/electrostrictive device as setforth in claim 8, wherein said movable plate is made of a conductivematerial.
 16. A piezoelectric/electrostrictive device as set forth inclaim 15, wherein said movable plate communicates with one of theexternal electrode layers of said piezoelectric/electrostrictiveelement.
 17. A piezoelectric/electrostrictive device as set forth inclaim 16, wherein said adhesive has conductivity, and wherein saidmovable plate communicates with one of the external electrode layers ofsaid piezoelectric/electrostrictive elements through the adhesive.
 18. Apiezoelectric/electrostrictive device in which a pair ofpiezoelectric/electrostrictive elements each includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes and in which saidpiezoelectric/electrostrictive elements are bonded to each other onsides of the respective narrower surfaces of said laminates.
 19. Apiezoelectric/electrostrictive device as set forth in claim 8, whereinsaid first and second external electrode layers are connected to avoltage applying circuit.
 20. A piezoelectric/electrostrictive device asset forth in claim 8, wherein said first and second external electrodelayers are connected to a voltage detecting circuit.
 21. A method ofproducing a piezoelectric/electrostrictive element comprising the stepsof: a first step of preparing a ceramic substrate having a given width;a second step of forming a laminate on said ceramic substrate, saidlaminate being made up of a first and a second portions laid to overlapeach other, the first portion being made by the steps of: printing afirst electrode layer and a second electrode layer on said ceramicsubstrate which are disposed at a given interval away from each other;forming a piezoelectric/electrostrictive layer using apiezoelectric/electrostrictive paste on the first and second electrodelayers so as to cover portions of the first and second electrode layersother than edge portions thereof lying outward in a widthwise directionof said ceramic substrate; forming a first electrode layer on an uppersurface and a side surface of the piezoelectric/electrostrictive layerso as to establish an electric connection only with the first electrodelayer lying immediately beneath the first electrode layer formed in thisstep, said second portion being made by performing the following set ofsteps a given number of times which include: forming apiezoelectric/electrostrictive layer using apiezoelectric/electrostrictive paste on an uppermost one of the firstelectrode layers, the piezoelectric/electrostrictive layer formed inthis step having a width smaller than that of thepiezoelectric/electrostrictive layer lying immediately beneath thepiezoelectric/electrostrictive layer formed in this step; forming asecond electrode layer on an upper surface and a side surface of anuppermost one of the piezoelectric/electrostrictive layers so as toestablish an electric connection only with the second electrode layerlying immediately beneath the second electrode layer formed in thisstep; forming a piezoelectric/electrostrictive layer using apiezoelectric/electrostrictive paste on an uppermost one of the secondelectrode layers, the piezoelectric/electrostrictive layer formed inthis step having a width smaller than that of thepiezoelectric/electrostrictive layer lying immediately beneath thepiezoelectric/electrostrictive layer formed in this step; forming afirst electrode layer on an upper surface and a side surface of anuppermost one of the piezoelectric/electrostrictive layers so as toestablish an electric connection only with the first electrode layerlying immediately beneath the first electrode layer formed in this step;and a third step of firing said ceramic substrate and said laminate at agiven temperature; and a fourth step of removing said laminate from saidceramic substrate.
 22. A method of producing apiezoelectric/electrostrictive element as set forth in claim 21, whereina width of the second electrode layer disposed on said ceramic substrateat a given interval away from said first electrode layer in an opposeddirection is greater than that of the first electrode layer.
 23. Amethod of producing a piezoelectric/electrostrictive element as setforth in claim 21, wherein a film is formed on said ceramic substratewhich disappears upon firing.
 24. A method of producing apiezoelectric/electrostrictive device in which apiezoelectric/electrostrictive element includes a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes, and the piezoelectric/electrostrictiveelement is bonded to a surface of a movable plate by adhesive.
 25. Amethod of producing a piezoelectric/electrostrictive device as set forthin claim 24, wherein said piezoelectric/electrostrictive elements arebonded to surfaces of said movable plate through adhesive.
 26. A methodof producing a piezoelectric/electrostrictive device in which a pair ofpiezoelectric/electrostrictive elements each include a substantiallytrapezoidal laminate having narrower and wider surfaces lyingsubstantially in parallel to each other and first and second surfacesopposed to each other between the narrower and wider surfaces, the firstand second surfaces being inclined at given angles to one of thenarrower and wider surfaces, said laminate being made up of a pluralityof piezoelectric/electrostrictive layers and a plurality of internalelectrodes each of which is disposed between adjacent two of thepiezoelectric/electrostrictive layers, the internal electrodes beingbroken up into a first and a second group, each of the first groupinternal electrodes lying over one of the second group internalelectrodes through one of the piezoelectric/electrostrictive layers; afirst external electrode formed on the first surface of said laminate,said first external electrodes being coupled to the first group internalelectrodes; and a second external electrode formed on the second surfaceof said laminate, said second external electrodes being coupled to thesecond group internal electrodes, and the piezoelectric/electrostrictiveelements are bonded to each other on sides of the respective narrowersurfaces of said laminates through adhesive.